1. Field of the Invention
The present invention relates to new aqueous suspensions of mineral fillers intended, for example, for the paper industry and the use thereof in the manufacture of paper and in the manufacture of coating color for paper.
2. Discussion of the Background
In practice, aqueous suspensions of mineral fillers, the rheology of which is such that it facilitates their use, are used as part of the process of manufacturing sheet paper and cardboard by mixing them with aqueous suspensions of cellulose fibers in order to improve the opacity, whiteness or printability of the paper produced.
They are also used in all applications during which the paper is coated, and are so in the form of aqueous compounds referred to as coating colors, essentially made up of water, binders and pigments or mineral fillers.
These pigments or mineral fillers, which may of various origins, have a different affinity to water depending on their nature. A first category consists of mineral substances with a charged hydrophilic surface such as natural or synthetic calcium carbonates, in particular chalks, calcites or marbles, the dolomites or alternatively kaolins as well as calcium sulphate or titanium oxides, satin white, aluminium hydroxides or others, for example. A second category covers mineral fillers with a hydrophobic surface such as talc, mica or others, for example.
Although these two types of mineral substances do not exhibit the same rheological behavior when placed in suspension in water, particularly when prepared in high concentrations, they must nevertheless exhibit the same quality criteria for the user. The aqueous suspensions of mineral substances must therefore possess a sufficiently yield stress to avoid all risk of sedimentation as well as a high enough but not too high Brookfield viscosity to prevent any hardening of particles of the mineral substances, so that they will be easy for the user to handle even after storage in tanks for several days without agitation. Furthermore, these suspensions must have as high a content of mineral substance as possible in order to reduce all the costs inherent in transportation due to the quantity of water present.
Previously, suspensions of mineral substances with a charged hydrophilic surface have conventionally contained dispersing agents or crushing aids consisting of polyacrylates. with a low molecular weight (EP 100 947, EP 542 643, EP 542 644). However, these agents have a disadvantage in that they are not very efficient when placing in suspension and/or crushing hydrophobic substances, such as talc or mica, which are commonly used alone or in mixtures. One skilled in the art currently uses suspensions of minerals with a hydrophobic surface containing other dispersing agents and/or crushing aids, these being copolymers in which one of the monomers has a surface-active structure (EP 0 003 235, EP 215 565). These copolymers, however, have a disadvantage in that they are not efficient when it comes to placing in suspension and/or crushing mineral substances with a hydrophilic surface such as the calcium carbonates or kaolins, calcium sulphate, titanium oxides, satin white, aluminium hydroxides or others.
Consequently, until now, in order to disperse and/or crush a mineral substance with a hydrophobic surface, it has been extremely difficult for the skilled person to use a dispersing and/or crushing agent known for its efficiency in dispersing and/or as an aid for crushing mineral substances with a hydrophilic surface and vice versa.
Faced with this problem of using dispersing agents and/or a crushing aid specific to a type of mineral substance, the applicant has conducted extensive research and has developed new suspensions of mineral pigment fillers which, irrespective of the nature of the mineral substance, have the same Theological properties and contain the same dispersing agent and/or crushing aid.
One of the objects of the present invention, therefore, is to obtain aqueous suspensions of mineral substances that are easy for the user to handle and can be used in the paper industry, regardless of whether these mineral substances have charged hydrophilic surfaces or hydrophobic surfaces.
Another object of the invention is the use of these aqueous suspensions of mineral fillers as proposed by the invention in the manufacture of paper and coating colors for paper.
The objects of the present invention, and others, may be accomplished by using as a dispersing agent and/or crushing aid a copolymer which contains the following monomers in polymerized form:
(a) at least one ethylenically unsaturated monomer having at least one carboxyl function,
(b) optionally, at least one ethylenically unsaturated monomer having at least one sulphonic and/or phosphoric function,
(c) optionally, at least one ethylenically unsaturated monomer which has no carboxyl function, and
(d) at least one surface-active, oxyalkylated, ethylenically unsaturated monomer ending with a hydrophobic chain, the radical of which is selected with a view to using the copolymer as a dispersing agent and/or crushing aid regardless of the type of mineral substances to be dispersed and/or crushed.
Monomer (d) is represented by the formula: 
where
m is at most 100,
p is at most 100,
n is at most 100,
q is a number at least equal to 1 and such that 0xe2x89xa6q (n+m+p)xe2x89xa6100,
R1 is hydrogen or a methyl or ethyl radical,
R2 is hydrogen or a methyl or ethyl radical.
R is a polymerizable unsaturated radical derived from an acrylic, methacrylic, maleic, itaconic, crotonic, or vinylphthalic ester or an unsaturated urethane, and
Rxe2x80x2 is a hydrophobic radical.
Accordingly, the present invention provides for an aqueous suspension comprising water, at least one mineral substance, in addition to the copolymer described above.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.
In one embodiment, the aqueous suspensions of mineral substances of the invention, which meet the above-mentioned quality criterion, are characterized in that the copolymer, dispersing agent and/or crushing aid contains:
(a) at least one ethylenically unsaturated monomer having a carboxyl function, selected from among the mono-acids such as acrylic, methacrylic, crotonic, isocrotonic or cinnamic acid, the diacids such as itaconic, fumaric, maleic or citraconic acid, the anhydrides of carboxylic acids such as maleic anhydride and the hemi-esters of diacids such as the monoesters at C1-C4 of maleic or itaconic acids, or mixtures thereof,
(b) optionally, at least one ethylenically unsaturated monomer having a sulphonic function, selected from among acrylamido-methyl propane-sulphonic acid, sodium methallylsulphonate, the vinyl sulphonic acids and styrene sulphonic acids, or having a phosphoric function selected from among ethylene glycol methacrylate phosphate, propylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate, propylene glycol acrylate phosphate and their ethoxylates, or mixtures thereof,
(c) optionally, at least one ethylenically unsaturated monomer having no carboxyl function, selected from the group comprising the esters of acrylic or methacrylic acids such as the methyl, ethyl, butyl, 2-ethyl-hexyl acrylates or methacrylates or acrylonitrile, methacrylonitrile, vinyl acetate, styrene, methylstyrene, diisobutylene, vinylpyrrolidone, vinylcaprolactam, or alternatively the unsaturated amides such as acrylamide, methacrylamide or their substituted derivatives such as, for example, dimethylaminopropyl acrylamide or methacrylamide, the acrylic or methacrylic esters of glycol, methacrylamidopropyl-trimethyl-ammonium chloride or sulphate, methacrylate of trimethylammonium-ethyl chloride or sulphate as well as their acrylate and quaternized acrylamide counterparts and/or dimethyldiallylammonium chloride, and
(d) at least one ethylenically unsaturated oxyalkylated monomer terminating with a hydrophobic chain having the general formula (I): 
in which:
m and p represent a number of alkylene oxide units and are each, independently less than or equal to 100,
n represents a number of ethylene oxide units and is less than or equal to 100,
q is a number at least equal to 1 and such that:
0xe2x89xa6q (n+m+p)xe2x89xa6100,
R1 is hydrogen or a methyl or ethyl radical,
R2 is hydrogen or a methyl or ethyl radical.
R represents a polymerizable unsaturated radical derived from the group of acrylic, methacrylic, maleic, itaconic, crotonic, vinylphthalic esters as well as the unsaturated urethanes such as, for example, acrylurethane, methacrylurethane, xcex1-xcex1xe2x80x2 dimethyl-m-isopropenyl-benzylurethane, or allylurethane.
Rxe2x80x2 represents the hydrophobic radical such as a tristyrylphenyl group or the linear or branched alkyl, alkylaryl, arylalkyl, aryl groups having at least 8 carbon atoms or the dialkyl amines having at least 8 carbon atoms when R represents the unsaturated urethanes, or Rxe2x80x2 represents the hydrophobic radicals such as tristyrylphenyl as well as the linear or branched alkyl, alkylaryl, arylalkyl, aryl groups having more than 30 carbon atoms or dialkylamines having more than 22 carbon atoms when R represents the polymerizable unsaturated radical belonging to the group of acrylic, methacrylic, maleic, itaconic, crotonic, vinylphthalic esters. In the copolymer, the total weight of the constituents (a), (b), (c) and (d) is equal to 100% and the copolymer has a specific viscosity at most equal to 50 and preferably at most equal to 25.
In a more preferred embodiment, the aqueous suspension of mineral substances proposed by the invention contains a copolymer as a dispersing agent and/or crushing aid that contains:
(a) from 99 to 10% by weight, and even more particularly for reasons inherent in the polymerization process from 97% to 50% by weight, of at least one ethylenically unsaturated monomer having a carboxylic function, selected from among the mono-acids such as acrylic, methacrylic, crotonic, isocrotonic, cinnamic acid, the diacids such as itaconic, fumaric, maleic, citraconic acid, or the carboxylic acid anhydrides such as maleic anhydride and the hemi-esters of diacids such as the monoesters at C1-C4 of maleic or itaconic acids or mixtures thereof,
(b) from 0 to 50% of at least one ethylenically unsaturated monomer having a sulphonic function selected from among acrylamido-methyl-propane-sulphonic acid, sodium methallylsulphonate, the vinyl sulphonic acids and styrene sulphonic acids, or having a phosphoric function selected from among ethylene glycol methacrylate phosphate, propylene glycol methacrylate phosphate, ethylene glycol acrylate phosphate, propylene glycol acrylate phosphate and their ethoxylates or mixtures thereof,
(c) from 0% to 50% by weight of at least one ethylenically unsaturated monomer having no carboxylic function, selected from the group comprising the acrylic or methacrylic acid esters such as the methyl, ethyl, butyl, 2-ethyl-hexyl acrylates or methacrylates or acrylonitrile, vinyl acetate, styrene, methylstyrene, diisobutylene, vinylpyrrolidone, vinylcaprolactam, or the unsaturated amides such as acrylamide, methacrylamide or the unsaturated amides such as acrylamide, methacrylamide or their substituted derivatives, such as for example dimethylaminopropyl acrylamide or methacrylamide, the acrylic or methacrylic esters of glycol, methacrylamido-prodyltrimethyl ammonium chloride or sulphate, the methacrylate of trimethyl-ammonium-ethyl chloride or sulphate as well as their acrylate and quatemised acrylamide counterparts and/or dimethyldiallylammonium chloride,
(d) from 1% to 90% by weight, and even more particularly for reasons pertaining to the polymerization process, from 3% to 50% by weight of at least one ethylenically unsaturated oxyalkylated monomer terminating with a hydrophobic chain, of the general formula (I): 
in which:
m and p represent a number of alkylene oxide units and is less than or equal to 100,
n represents a number of ethylene oxide units and is less than or equal to 100,
q is a number at least equal to 1 and such that: 0xe2x89xa6q(n+m+p)xe2x89xa6100,
R1 is hydrogen or a methyl or ethyl radical,
R2 is hydrogen or a methyl or ethyl radical.
R represents a polymerizable unsaturated radical belonging to the group of acrylic, methacrylic, maleic, itaconic, crotonic, vinylphthalic esters as well as the unsaturated urethanes such as, for example, acrylurethane, methacrylurethane, xcex1-xcex1xe2x80x2 dimethyl-m-isopropenyl-benzylurethane, allylurethane.
Rxe2x80x2 represents the hydrophobic radical such as tristyrylphenyl group or the linear or branched alkyl, alkylaryl, arylalkyl, aryl groups having at least 8 carbon atoms or the dialkyl amines having at least 8 carbon atoms when R represents the unsaturated urethanes or Rxe2x80x2 represents the hydrophobic radicals such as tristyrylphenyl as well as the linear or branched alkyl, alkylaryl, arylalkyl, aryl groups having more than 30 carbon atoms or dialkylamines having more than 22 carbon atoms when R represents the polymerizable unsaturated radical belonging to the group of acrylic, methacrylic, maleic, itaconic, crotonic, vinylphthalic esters,
where the sum of the weight percents monomers (a), (b), (c) and (d) in the polymer is equal to 100% and in that the copolymer has a specific viscosity at most equal to 50, and preferably at most equal to 25.
In monomer (d), the variables m and p represent the number of alkylene oxide units. I d These variables are each, independently, less than or equal to 100 (at most 100). The variables m and p may, independently, be 0, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 75, 85, 90, 95, 97 and 99, inclusive of all specific values and subranges therebetween.
The variable n represents the number of ethylene oxide units and is less than or equal to 100 (i.e., at most 100). The variable n may be 0, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 75, 85, 90, 95, 97 and 99, inclusive of all specific values and subranges therebetween.
In the copolymer the amount of monomer (a) may be 10 to 99% by weight. This range includes all specific values and subranges therebetween, including 15, 20, 25, 30, 35, 40, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 97 and 98% by weight.
The amount of monomer (b) in the copolymer may be 0 to 50% by weight. This range includes all specific values and subranges therebetween, including 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40 and 45% by weight.
The amount of monomer (e) in the copolymer may be 0 to 50% by weight. This range includes all specific values and subranges therebetween, including 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40 and 45% by weight.
The amount of monomer (c) in the copolymer may be 1 to 90% by weight. This range includes all specific values and subranges therebetween, including 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 65, 70, 75, 80 and 85% by weight.
The copolymer may be obtained by known methods of radical copolymerization in solution, in direct or inverse emulsion, in suspension or precipitation in appropriate solvents in the presence of known catalytic systems and transfer agents, using well-known procedures.
This copolymer, obtained in acid form and possibly distilled, may be partially or totally neutralized by one or more neutralizing agents having a monovalent function or a polyvalent function such as, for example, those selected from the group comprising the alkaline cations, in particular sodium, potassium or ammonium or alternatively the primary, secondary or tertiary aliphatic and/or cyclic amines such as, for example, stearylamine, the ethanolamines (mono-, di-triethanolamine), mono- and diethyl amine, cyclohexylamine, methylcyclohexylamine or those selected from the group comprising the divalent alkaline earth cations, in particular magnesium and calcium or alternatively zinc, as well as the trivalent cations, including in particular aluminum, or alternatively certain cations with a higher valency. Each neutralizing agent is used in a quantity suited to the neutralization rates appropriate to each valency function. Once obtained, this copolymer can be used in the totally acid form or partially neutralized or fully neutralized.
In another variant, the copolymer produced by the copolymerization reaction may be treated and separated into several phases, either before or after the total or partial neutralization reaction, using the static or dynamic processes familiar to the person skilled in the art, by one or more polar solvents belonging in particular to the group comprising water, the alcohols such as methanol, ethanol, propanol, isopropanol, the butanols, the ketones, such as, in particular, acetone, methyl-ethyl ketone, cyclohexanone or alternatively tetrahydrofuran, dimethylsulphoxide or mixtures thereof.
One of the phases then corresponds to the copolymer contained in the aqueous suspension of mineral substances as proposed by the invention.
The specific viscosity of the copolymer is symbolized by the letter xe2x80x9cxcex7xe2x80x9d and is determined in the following way:
A polymer solution is made up to obtain a solution corresponding to 2.5 g of dry polymer neutralized with soda and 50 ml of a bipermutated water solution. Using a capillary viscometer with a Baume constant equal to 0.000105 placed in a bath thermostatically controlled to 25xc2x0 C., a measurement is taken of the flow time of a given volume of the above-mentioned solution containing the polymer as well as the flow time of the same solution of bipermutated water without the said copolymer. It will then be possible to define the specific viscosity xe2x80x9cxcex7xe2x80x9d by means of the following equation:             xe2x80x83        ``    ⁢      η    xe2x80x3    =                                                        (                              flow                ⁢                                  xe2x80x83                                ⁢                time                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                the                                                                                                        polymer                ⁢                                  xe2x80x83                                ⁢                solution                            )                                          -                                                  (                              flow                ⁢                                  xe2x80x83                                ⁢                time                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                the                                                                                                        permutated                ⁢                                  xe2x80x83                                ⁢                water                ⁢                                  xe2x80x83                                ⁢                solution                            )                                                  flow      ⁢              xe2x80x83            ⁢      time      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      the      ⁢              xe2x80x83            ⁢      permutated      ⁢              xe2x80x83            ⁢      water      ⁢              xe2x80x83            ⁢      solution      
The capillary tube is generally selected so that the flow time of the permutated water solution without the copolymer is approximately 90 to 100 seconds, thus giving highly accurate specific viscosity readings.
The mineral substances (e.g., mineral fillers) used in the invention are of very diverse origins and can be classified in two general categories.
The first category is made up of mineral substances with a charged hydrophilic surface such as the natural or synthetic calcium carbonates, for example, particularly chalks, calcites, marbles or dolomites or alternatively the kaolins, calcium sulphate, titanium oxides or satin white or aluminum hydroxides or any other mineral with a hydrophilic surface. The second category includes mineral fillers with a hydrophobic surface such as, for example, talc, mica and any other mineral with a hydrophobic surface.
Apart from the copolymer used as a dispersing agent and/or crushing aid, this aqueous suspension of mineral substances is characterized in that said mineral substance or substances are selected either from the mineral substances with a charged hydrophilic surface such as the natural or synthetic calcium carbonates, in particular chalk, calcite, marble or dolomite or the kaolins, calcium sulphate, titanium oxides or mixtures thereof, or are selected from the mineral substances with a hydrophobic surface such as, talc or mica or mixtures thereof in particular, or alternatively a mixture of mineral fillers with a hydrophilic surface and mineral fillers with a hydrophobic surface.
In practice, one way of dispersing the mineral substance or substances to be dispersed consists in preparing, under agitation, an aqueous solution of the dispersing agent proposed by the invention to which the mineral substance or substances to be dispersed are added.
For the purposes of the invention, the dispersing agent is introduced in a quantity of from 0.05% to 5% by weight of the dried fraction of said polymers relative to the dry weight of the mineral substance or substances to be refined. This weight range includes all specific values and subranges therebetween, including 0.1, 0.2, 0.5, 1, 2, 3 and 4% by weight.
Similarly, in practice, the operation of crushing the mineral substance or substances to be refined consists in crushing the mineral substance or substances with a crushing medium in very fine particles in an aqueous medium containing the crushing agent. An aqueous suspension of the mineral substance or substances to be crushed is then formed.
The crushing medium added to the suspension of the mineral substance or substances to be crushed advantageously has a grain size of between 0.20 and 4 millimeters. The crushing medium is generally present in the form of particles of substances as diverse as silicon oxide, aluminum oxide, zirconium oxide or mixtures thereof as well as the very hard synthetic resins, steels or others. An example of a composition for such crushing media is given in patent FR 2 303 681, incorporated herein by reference, which describes crushing media made up of 30 to 70% by weight of zirconium oxide, 0.1 to 5% of aluminum oxide and from 5 to 20% of silicon oxide. By preference, the crushing medium is added to the suspension in a quantity such that the ratio by weight of this crushing medium to the mineral substance or substances to be crushed is at least 2/1, this ratio preferably being within the ranges of 3/1 and 5/1.
The mixture of the suspension and the crushing medium is then subjected to mechanical agitation, such as that produced in a conventional crusher with micro-elements.
In accordance with the invention, the dispersing agent and/or crushing aid is also introduced to the mixture comprising the aqueous suspension of mineral substances and the crushing medium in a quantity of 0.05% to 5% by weight of the dried fraction of said polymers relative to the dry weight of the mineral substance or substances to be refined.
The time needed to produce an excellent fineness of the mineral substances after crushing will depend on the nature and quantity of the mineral substances to be crushed as well as on the agitation method used and the ambient temperature during the crushing operation.
If the mineral substance or substances are one or more mineral substances with a hydrophilic surface, the aqueous suspension of mineral substances proposed by the invention will also have a high yield stress as well as a low Brookfield viscosity with high contents of dry substance, i.e., at least 45% and preferably at least 60%.
If the mineral substance or substances are one or more mineral substances with a hydrophobic surface, the aqueous suspension of mineral substances proposed by the invention will have a high yield stress and a low Brookfield viscosity with high contents of dry substance, i.e., at least 45% and preferably at least 60%.
Similarly, if the mineral substances are a mixture of mineral substances with a hydrophilic surface and mineral substances with a hydrophobic surface, the aqueous suspension of mineral substances proposed by the invention will have a high yield stress and a low Brookfield viscosity with high contents of dry substance, i.e., at least 45% and preferably at least 60%.
The particle size of the mineral substance in the suspension is such that 90% of the particles have a diameter of less than 2 micrometers.
The suspension preferably contains at least 5% by weight of the mineral substance(s). The suspension may contain, for example, at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 and 85% by weight, inclusive of all specific values and subranges therebetween.
The above-mentioned rheological properties of the aqueous suspensions of mineral substances proposed by the invention make them suitable for use in the paper industry, particularly as a mass filler for paper or as an essential component in coating colors.
The coating colours of the invention are prepared in a manner known to the person skilled in the art by mixing suspensions of mineral fillers of the invention with water and one or more binders of natural or synthetic origin such as, for example, starch, carboxymethyl cellulose, the polyvinyl alcohols or alternatively latex of the styrene butadiene or styrene acrylate type or alternatively latex of the acrylic, vinyl or other types.
The coating colours can contain, in a manner known to the person skilled in the art, usual additives such as rheology modifiers, organic fillers, antifoam agents, optical brighteners, biocides, lubricants, alkaline hydroxides and others.